As a method for manufacturing an acrylic acid, a method is commonly known which involves collecting, in a collection solvent such as water, an acrylic-acid-containing gas resulting from gas-phase catalytic oxidation using propane, propylene or acrolein as a material, separating an acrylic acid from the resultant acrylic acid solution, and purifying the separated acrylic acid by vacuum distillation.
Furthermore, as a method for manufacturing an acrylic ester, for example, a method is known which involves causing esterification between a purified acrylic acid and alcohol to obtain a crude acrylic ester and distilling and purifying the crude acrylic ester, or causing transesterification between an acrylic ester and alcohol to obtain a crude acrylic ester and distilling and purifying the resultant crude acrylic ester.
Acrylic acids are easily polymerizable compounds. Polymerization is likely to occur in a purification process for a solution of acrylic acids, particularly a distillation process involving a large amount of heating. Thus, to prevent polymerization of acrylic acids in a distillation column, a method is used which involves supplying a polymerization inhibitor or molecular oxygen or decompressing the inside of the distillation column in order to reduce the temperature in the distillation column.
Distillated gas from the distillation column is cooled and condensed by a heat exchanger, and a portion of uncondensed gas is sucked into a decompression apparatus. As the decompression apparatus, a liquid seal vacuum pump or a steam ejector is commonly used. However, the uncondensed gas also contains an acrylic acid, and thus, polymerization of the acrylic acid may occur around the decompression apparatus.
Patent Literature 1 (Japanese Patent Application Laid-open No. 2000-344711) discloses a method in which, in the above-described case, the gas sucked into the steam ejector is discharged from the steam ejector along with driving steam and in which, during the subsequent cooling, a polymerization-inhibitor-containing liquid is supplied.
Furthermore, Patent Literature 2 (Japanese Patent Application Laid-open No. 2005-289927) discloses a method in which the steam and the sucked gas discharged from the steam ejector are cooled to lower than 40° C. with no addition of a polymerization inhibitor to prevent polymerization of the acrylic acid in the condensed liquid.